Cryptology ePrint Archive: Report 2004/234

On the security of some nonrepudiable threshold proxy signature schemes with known signers

Zuo-Wen Tan and Zhuo-Jun Liu

Abstract: A (t,n) threshold proxy signature scheme enables an original signer
to delegate the signature authority to a proxy group of n member
such that t or more than t proxy signers can cooperatively
sign messages on behalf of the original signer. In the paper, we
review the security of some nonrepudiable threshold proxy
signature schemes with known signers. We show that Sun's threshold
proxy scheme, Yang et al.'s threshold proxy signature scheme and
Tzeng et al.'s threshold proxy signature scheme are insecure
against an original signer's forgery. We also show that Hsu et
al.'s threshold proxy signature scheme suffers from the conspiracy
of the original signer and the secret share dealer SA, and that
Hwang et al.'s threshold proxy signature scheme is universally
forgeable. In a word, none of the above-mentioned threshold proxy
signature schemes can provide non-repudiation.